This invention relates to windshield wiper devices for vehicles, and more particularly it is concerned with a windshield wiper device which avoids separation of the wiper blade from the pane of the windshield when the vehicles travels at high speed.
A windshield wiper for wiping the pane of a windshield of a vehicle is exposed to the high pressure of winds when the vehicle travels at high speed. As a result, the wiper blade tends to separate itself from the pane during its reciprocatory movement, particularly during its return movement, across the surface of the windshield. This results in the surface of the windshield being unsatisfactorily wiped which blocks the line of sight of the driver, thereby seriously interfering with the manipulation of the vehicle by the driver. Separation of the wiper blade from the surface of the windshield, particularly during its return movement, is attributed to the fact that the velocity of the wind blowing against the wiper blade during its return movement is equal to the sum of the vehicle speed and the speed of oscillating movement of the wiper blade.
Various proposals have hitherto been made for avoiding separation of the wiper blade from the surface of the windshield. In one proposal, the resilient force of a spring of the windshield wiper device is increased, to increase the force with which the blade rubber is forced against the pane of the windshield. When such proposal is incorporated in a windshield wiper, frictional dragging of the blade rubber on the surface of the pane would naturally increase and it would necessary to use a powerful motor (of large size that consumes a great deal of electricity) for driving the wiper blade. In addition, when the vehicle travels at low speed or remains stationary or when it travels in drizzling weather, the windshield wiper would chatter when operated to wipe the pane, so that normal wiping of the pane would be unobtainable.
In another proposal known in the art, a vane-like member is attached to the support metal fixture or support arm of the blade to cause a force urging the blade rubber to press against the pane (reverse lift) to be produced from the pressure of the wind blown against the vane-like member, so that the produced force and a force tending to cause the blade to separate itself from the vane will cancel each other out. It would theoretically be possible to cause a force tending to urge the blade rubber to press against the pane which is commensurate with the velocity of the wind blown against the pane. However, the direction in which the wind blows in front of the windshield and the velocity of such wind are not uniform and simple but irregular and multitudinous, and the blade itself is not stationary but oscillates. Thus when the wiper is provided with the aforesaid vane-like member, it might be possible to achieve satisfactory results only when the angle of elevation thereof suits the prevailing conditions, but the vane-like member might be agitated by the wind when the vehicle speed and the direction of wind are unfavorable, with a result that the vane-like member might flap in the wind and the blade might separate itself from the surface of the windshield or chatter. Under such circumstances, it would be impossible to carry out a wiping operation satisfactorily. Also, when the vane-like member attached to the blade is large in size, visibility would become poor and an increase in the weight of the wiper would raise problems in fabrication and operation.